The invention relates to methods for producing superoxide ions in situ. Specifically, the methods involve the use of a solution of dissolved dioxygen in an aprotic solvent, a compound that provides hydroxide ions in the solution, and a hydrogen donor or proton donor. The hydrogen donor or proton donor reacts with the hydroxide ions and dioxygen in the solution of an aprotic solvent to generate superoxide ions. An anthraquinone catalyst has proven effective to promote the reaction for certain hydrogen donors which otherwise do not react with the hydroxide ions and dioxygen to generate superoxide ions.
Superoxide ions have proven useful in many applications. Superoxide ions are an effective nucleophile in aprotic media. Sugimoto et al. J. Am. Chem. Soc. 1988, 110, 5193. Further, biochemists have studied superoxide ions because they are respiratory intermediates. Knowles et al. Biochem. J. 1969, 111, 53.
Superoxide ions have proven particularly effective for destroying halogenated hydrocarbons such as polychlorinated biphenyls (PCBs) and similar toxic materials that create environmental hazards. U.S. Pat. Nos. 4,468,297 and 4,410,402, describe the use of superoxide ions for degrading halogenated hydrocarbons and halogenate olefinic hydrocarbons.
The destruction of halogenated hydrocarbons has proven difficult. Many of these compounds react slowly or incompletely with traditional bases; this becomes a significant problem as the number of halogen atoms in the compound increases (U.S. Pat. No. 4,410,402, col. 1, lines 35-41). Superoxide ions overcome this difficulty, and react rapidly with halogenated hydrocarbons when the reaction is carried out in an aprotic solvent. (U.S. Pat. No. 4,410,402, col. 2, lines 34-52).
Several methods have been developed to generate superoxide ions. For example, pulse radiolysis of dioxygen has been used to generate superoxide ions Gebicki et al. J. Am. Chem. Soc. 1982, 104, 796. Further, photolysis of hydrogen peroxide in aqueous media, and base-induced decomposition of hydrogen peroxide have also been used to generate superoxide ions. McDowell et al. Inorg. Chem. 1983, 22, 847; and Morrison et al. Inorg. Chem. 1979, 18, 1971.
Solutions of superoxide ion in aprotic solvents have also been prepared using electrochemical means. Sawyer et al. Anal. Chem. 1982, 54, 1720. For example, the superoxide ions used for degrading halogenated hydrocarbons in U.S. Pat. Nos. 4,468,297 and 4,410,402, are generated in a controlled potential electrolysis cell which uses aprotic solvent for the electrolyte. (U.S. Pat. No. 4,410,402, col. 2, lines 53-57; U.S. Pat. No. 4,468,297, col. 2, lines 44-48).
The methods described above for generating superoxide ions suffer from several disadvantages and are not appropriate for all applications. For example, methods for generating superoxide ions based on pulse radiolysis, photolysis, or electrolysis, all require radiation or electrical energy sources. Typically, the energy costs for these methods are prohibitively expensive, especially for applications such as degrading halogenated hydrocarbons on an industrial scale. Likewise, methods for generating superoxide ions based on decomposing hydrogen peroxide may be prohibitively expensive for particular applications due to the cost of hydrogen peroxide. Consequently, other methods for generating superoxide ions are desired.